Key Engineering Materials Vols. 297-300

Abstract: A sudden failure of the bearing of the turbocharger shaft in a diesel engine, with the power of 11520KW and the total running time of 2,417h, is investigated in this paper. Based on an examination of the disassembled turbocharger and a residue analysis, it was found that the failure of the turbocharger originated from a fatigue fracture of an aluminum-alloy bearing retainer (cage) on its compressor side. The axial load was a chief cause of the fatigue fracture and the looseness defects in the aluminum alloy retainer deteriorated its fatigue strength which in turn accelerated the development of fatigue cracks. After the retainer broke, the off-centered rotation of the turbocharger shaft triggered a severe impact and led to deformation, wear and a fracture of the bearing parts, ultimately resulting in the failure of the turbocharger.

Abstract: In contact conditions of crane sheave steel materials against a wire rope, the contact surface of the sheave generally exhibits scuff damage. In the present study, sliding wear tests using annealed-low carbon cast steel were carried out under three kinds of normal loads calculated from the actual model conditions in a pin-on-disk grease lubrication test. The sliding speed was fixed at 220mm/s. Therefore, the wear behavior and wear mechanism and the residual stress distribution of the substrate surface were examined. The results of this study indicate that the wear rate of annealedlow carbon cast steel depends on the diameter of the wires. The wear mechanism of annealed-low carbon cast steel is characterized by fatigue and abrasive wear, but the wire shows partial adhesion due to micro abrasive wear by fatigue crack propagation. The contact distribution of residual stress is independent of sliding distance. Therefore, there are constant values on the contact surface.

Abstract: In this paper, the effects of the residual stresses on the life of structural engineering components were investigated to predict the wear-life. Residual stresses are usually created by the surface treatment, such as shot peening or deep rolling. The objective of the experimental investigation was focused on the influence of friction and wear characteristics due to the residual stress under dry sliding condition and the measurement of the interleaf friction. Test specimens were made of SUP9, the leaf spring material. The residual stresses were created on their surface by shot peening treatment. Residual stress profiles were measured on the surface and subsurface by means of X-ray diffraction method. Also, the sliding tests were carried out under the different contact pressure and the same sliding velocity of 0.035m/s in order to investigate the friction and wear characteristics of leaf surfaces. Leaf spring assembly tests were performed by the ultimate tensile machine with sticking strain gauges on the leaf surfaces in order to evaluate interleaf friction characteristics. We compared friction coefficients, wear volumes and wear rates of the shot-peened specimens with those of the unpeened specimens, and evaluated the effects of residual stress on the tribological characteristics. We obtained the load-displacement curves, and measured interleaf friction force and interleaf friction coefficient of leaf spring assembly from these curves.

Abstract: In this study, the variation of spring characteristics with increasing temperature was examined and the effect of their variations on the wear behavior of a nuclear fuel rod in both room and high temperature (300°C) water conditions was evaluated. From the results of the load-displacement tests, the spring stiffness was remarkably varied with increasing temperature. The results of the wear tests indicated that the wear damages are decreased at high temperature water when compared with the room temperature result. These results indicated that the removal mechanisms of wear debris at high temperature water are dependent on not only the formation of the wear particle layer but also on the changed contact conditions such as the contact length or area due to the stiffness drops.

Abstract: Application of powder boronizing to mechanical industry has been restricted because of the brittleness of boronized layer, which inevitably leads to decrease of service life of boronized parts. Therefore, attention should be paid to reducing the brittleness of boronized layer without decreasing its high hardness. In the present paper, a study on the effect of micro-addition rare earth and chrome on friction and wear behavior of boronized layer was carried out using an MM-200 wear test machine. Compared with that of pure single Fe2B phase, the brittleness of the boronized layer containing minim rare earth and chrome elements, obtained by powder RE-chrome-boronizing, is reduced, which results in increasing the bearing capacity and wear resistance of the boronized layer. The friction and wear mechanism is also briefly analyzed.

Abstract: Fretting is the oscillatory motion with very small amplitudes, which usually occurs between two solid surfaces in contact. Fretting wear is the removal of material from contacting surfaces through fretting action. Fretting wear of steam generator tubes in nuclear power plant becomes a serious problem in recent years. The materials for the tubes usually are INCONEL 690 (I-690) and INCONEL 600 (I-600). In this paper, fretting wear tests for I-690 and I-600 were performed under various applied loads in water at room temperature. Results showed that the fretting wear loss of I-690 and I-600 tubes was largely influenced by stick-slip. The fretting wear mechanisms were the abrasive wear in slip regime and the delamination wear in stick regime. Also, I-690 had somewhat better wear resistance than I-600.

Abstract: In steam generators of nuclear power plants, flow-induced vibration (FIV) can lead to tube damage by fretting-wear occurred due to impact and sliding movement between the tubes and their supports. There have been many studies and test results on wear damage of steam generator tubes but they were not reflected the mechanical and chemical conditions accurately. KEPRI nuclear power laboratory developed a wear test system, which is able to control the motion of impact and sliding simultaneously in the pressurized high temperature water-chemistry conditions. Some wear tests were performed to verify the stable operation for the wear test. This wear test system with new concepts was described briefly, and some data for verifying its performance have been shown in the cases of the selected some test results. In the test, Alloy 690 was used for tube materials and 409 stainless steel for support plates. A little data deviation was obtained and stability of system operation was investigated.

Abstract: In this paper, the fretting wear characteristics of INCONEL 690 (I-690) and INCONEL 600 (I-600) was evaluated to verify the wear mechanism and the wear life. Because of the excellent corrosion-resistance of nickel-based alloy, those materials are used for steam generator tube in nuclear power plants. Sometimes the tubes are damaged due to small amplitude vibration, so called fretting wear. To verify the fretting wear mechanisms the wear experiment was carried with the crossed-cylinder wear tester, which used a cam to oscillate the specimen. The test was carried out at loads of 40N and 90N in elevated temperatures of water. The temperatures of water were 20°C, 50°C and 80°C. The increase of water temperature causes the oxidation of the contact area to be delayed, and the amount of wear on oxide layer to be reduced. The main wear mechanisms of fretting were abrasive wear and oxidation wear.

Abstract: Four different multilayered coatings with different Al concentrations were deposited on AISI D2 steel. The prepared coating samples were designated as WC-Ti0.6Al0.4N, WC-Ti0.53Al0.47N, WC-Ti0.5Al0.5N and WC-Ti0.43Al0.57N. The multilayered coatings were investigated with respect to coating surface and cross-sectional morphology, roughness, adhesion, hardness, porosity and tribological behavior. Especially, wear tests of four multilayered coatings were performed by using a ball-on-disc configuration with a linear sliding speed of 0.017 m/sec and a load of 5.38N. The tests were carried out at room temperature in air by employing AISI 52100 steel ball (HR = 66) with a diameter of 10mm. The surface morphology and topography of the wear scars of samples and balls have been determined by using scanning electron spectroscopy (SEM). Results have showed an improved wear resistance of the WC-Ti1-xAlxN coatings with increasing Al concentration.